It said there was increased risk of wound infections, dermatitis, conjunctivitis, and ear, nose and throat infections from polluted waters, but also highlighted the possibility of melioidosis, a disease caused by bacteria in soil, and leptospirosis, a serious illness caused by bacteria in animal urine.

It advised residents in Gayndah, Mundubbera, Atkinson Dam, Somerset Dam, Toowoomba, Condamine and Dalby to boil drinking water because supplies were unsafe.

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The warnings came as hospitals in Toowoomba, Ipswich, Caboolture, Gympie and Nambour cancelled elective surgery and other services yesterday because of the floods.

Vice-president of the Australian Medical Association Dr Steve Hambleton said there was increasing pressure on medical services across the state as hundreds of nursing home residents were being evacuated to other facilities and hospitals became inaccessible.

''I just tried to get a patient into a private hospital and it wasn't accepting any patients because it was basically an island next to the river. So I think there is going to be a lot of difficulties with medical staff getting to work,'' he said last night.

Professor Tony McMichael, from the Australian National University's Centre for Epidemiology and Population Health, said increasing numbers of mosquitoes breeding in the warm, wet conditions could cause fresh outbreaks of the potentially deadly dengue fever and debilitating Ross River virus in coming weeks. Murray River encephalitis, a mosquito borne disease that has a 10-20 per cent mortality rate, could also emerge.

Professor McMichael said dangerous industrial, agricultural and domestic chemicals in the flood waters may also be a problem if people accidentally inhale them or get them in their eyes.

''There's a pretty unholy mix of potential microbial and chemical contamination,'' he said.

In the longer term, Professor McMichael said Queensland could expect to see high rates of mental health problems in the affected communities. He said recent studies of flood-affected towns in Britain found up to three-quarters of the populations suffered mental health disorders after the crises.

''There will be a need for a lot of counselling … which will persist for many months, if not years,'' he said.

Acting Minister for Health and Ageing Mark Butler said although the Queensland government was working on immediate crisis-support counselling, the Commonwealth would work with it to boost low-cost and free access to psychologists in coming months.

Dr Ross Sadler, a senior lecturer in environmental health at Griffith University, said residents were also likely to face unsanitary conditions for many weeks after the flood waters recede, especially as sewage treatment plants are overwhelmed. ''I think problems with sewage will be enormous,'' he said.